Catalyst and process for preparation thereof



Unitcd States Patent 7 Claims. (Cl. 252-432 ABSTRACT OF THE DISCLOSURE Catalyst for oxidation of lower aliphatic olefins to produce saturated aliphatic products. The catalyst comprises calcined molybdenum oxide, bismuth oxide, phosphoric acid, and boric acid on a support such as silica or alumina. The phosphoric acid and boric acid, figured as P 0 and B 0 amount to about 1-25% of the total catalyst.

This application is a division of application Ser. No. 214,521, filed Aug. 3, 1962, now Patent 3,255,238.

The instant invention relates to a catalyst and a process for the production of the catalyst.

The catalyst is useful for oxidation of aliphatic olefins and permits selection with respect to the products of the oxidation. 'Use of the catalyst in oxidation reactions is the subject of Patent 3,255, 238 (Ser. No. 214,521, filed Aug. 3,1962).

It is known that acrolein can be produced by catalytic oxidation of aliphatic olefins such as propylene in the presence of oxygen. The reaction is eifected at temperatures in the range between about 200 and 500 C. with the use of atmospheric pressure or supcratmospheric pressure. The catalysts are selected from a great number of heavy metal oxides used alone or in mixture with one another, examples of suitable heavy metal oxides being copper oxide, silver oxide, chromium oxide, bismuth oxide, tungsten oxide, molybdenum oxide, etc. The reaction products obtained are mainly acrolein and small amounts of acetaldehyde. A process for the production of oxidation products as referred to here is disclosed in our co-pending application Ser. -No. 142,462, filed June 29, 1961.

It has been found that the catalytic oxidation of low molecular weight aliphatic olefins by contacting with oxygen at elevated temperatures can be carried out in a manner to provide as oxidation products materials which are saturated, if the catalyst is formed of heavy metal oxides as have been used heretofore (see above) and phosphoric acid and boric acid. The products of the oxidation can be saturated aldehydes, acids and esters.

The catalyst can be formed by a catalyst support hearing heavy metal oxide and phosphoric acid and boric acid activated while contained on the support by heating to above about 150 C.

The catalyst of the instant invention consists essentially of heavy metal oxide for oxidation of olefins, and phosphoric acid and boric acid deposited on a catalyst support. The amount of phosphoric acid and boric acid is about 1-25% of the total catalyst and the mol proportion of boric acid to phosphoric acid is in the range of about 5:1 to 1:5.

The catalyst can be produced by depositing phosphoric acid and boric acid on a catalyst support, and thereafter depositing on the support heavy metal oxide for oxidation of olefins.

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It has been found in experiments that the combination of phosphoric acid and boric acid, or boryl phosphate, in contrast to the use of phosphoric acid alone or boric acid alone, has the effect of suppressing substantially completely oxidation at the methyl group and of causing extensive oxidation at the double bond, e.g., of propylene. Consequently, acrolein is hardly found in the reaction products of the oxidation while formaldehyde, acetaldehyde, acetic acid and acetic ester are now obtained as the preferred reaction products.

Relatively small amounts of boric acid and phosphoric acid are sufiicient to obtain the effect desired, For example, about 1% of the acid mixture in the catalyst is completely sufficient to achieve the alteration of the catalytic characteristics mentioned above. Lesser amounts can be used. Also larger amounts can be used. The amount can be up to about 25% are preferably amounts of between 1.5% and 15%, based on total catalyst, are used. Total catalyst means catalyst inclusive of carrier.

The molar ratio of boric acid to phosphoric acid may be varied between about 5 :1 and 1:5. It is favorable if the molar amounts are not greatly different, e.g. 2.5 :1 to 1:25, or 2.5 :1 to 1:1. A particularly favorable composition is obtained when the molar ratio is about 1:1.

As has been indicated above, the heavy metal oxide can be a heavy metal oxide or a mixture of heavy metal oxides as are known for the oxidation of olefins to produce compounds such as acrolein. Thus, the heavy metal oxide can be an oxide of silver, copper, chromium, tungsten, molybdenum, bismuth, or a mixture of two or more of these oxides.

The preferred heavy metal oxide is a mixture of molybdenum oxide and bismuth oxide. In such a mixture, the mol proportion of molybdenum oxide to bismuth oxide shall be about 1:3-l:0.3. The amount of molybdenum oxide ranges from 5 to 60% by weight, dependent upon the weight of the total catalyst inclusive of the carrier, an amount of 10 to 37% being preferred.

Theca-talysts of the invention are preferably contained on a catalyst support. Various materials are known for service as catalyst supports, and, in general, such mate rials are suitable for the purposes of the invention. The preferred material for use as a support is silica. Desirably, the silica is fume silica of the type disclosed for use as a carrier support in our copending application Ser, No. 104,814, filed Apr. 24, 1961, now abandoned.

The acids and the heavy metal oxides may be applied to the support by soaking, spraying, precipitation, etc. It is possible to add the acids and oxides simultaneously or in succession. Catalysts having satisfactory properties are obtained in any case. However, the order of addition is of some importance in view of the optimum chacteristics of the catalyst. Preferably the phosphoric acid and boric acid are applied first.

The amounts desired of boric acid and phosphoric acid can be applied to the support from an aqueous solution by soaking, spraying, or evaporation, with two acids being incorporated in succession, simultaneously, or in stepwise fashion wherein portions of each are applied alternately. Another acid, such as dilute nitric acid, may be added to the aqueous solution of acids in small amounts.

This treatment is effected at a temperature ranging between room temperature and C. The water should be evaporated extensively, if necessary to dryness, before the heavy metal oxides are added.

The application of the boric acid-phosphoric acid mixture to the support is followed by soaking with the heavy metal oxide or oxides desired. This is likewise preferably effected by use of an aqueous medium. The corresponding salts can be dissolved in water, and small amounts of, for example, nitric acid can be added. Good results are already obtained if molybdic acid, e.g. in the form of ammoniurn molybdate, is used as theonly heavy metal oxide for the catalyst. An improvement in selectivity which, however, is accompanied by some increase in reaction temperature, can be obtained by adding certain amounts of bismuth oxide, e.g. in the form of bismuth nitrate, to the molybdenum oxide. In this case, satisfactory catalysts are obtained with a molybdenum oxide to bismuth oxide ratio of between about 1:3 and 1:03. However, other molar proportions are also applicable.

While ammonium molybdate is the preferred form of molybdic acid, the bismuth compound is preferably used in the form of bismuth nitrates. The compounds or mixtures to be used are dissolved in water, preferably with addition of small amounts of nitric acid, at temperatures of between about room temperature and 100 C., the pretreated carrier material is added and the whole mixture is evaporated to dryness. However, in place of direct soaking, it is possible to apply the solution of heavy metal salts to the carrier material by spraying or to use subatmospheric pressured during evaporation, etc.

One or mixtures of two and more of a great number of other heavy metal compounds such as those of silver, copper, chromium, tungsten, etc. may be used in place of two heavy metal compounds mentioned above. In place of soaking, it is also possible, for example, to deposit precipitates of the corresponding heavy metal salts with alkali metals or acids on the support.

After incorporation of all of the compounds desired in the carrier material and extensive drying or evaporation of the present water in a temperature range between about 50 and 150 C., the catalyst is molded. The molding operation is dependent upon the type of process in which the catalyst is to be used. For example, the simplest catalyst form is produced by granulation of the evaporated dry catalyst cake and recovering the fraction between about 2 and 6 mm. by screening with both oversized and undersized granules being returned to the catalyst preparation step. Other methods of molding the catalyst mass, e.g. the production of pellets with the use of a pellet mill, the production of compressed catalyst particles with the use of a press to prepare cylindrical or lens-shaped granules to be used.

After molding, and if desired, post-drying preferably effected in a temperature range of 50 to 150 C., the catalyst is preferably activated by thermal after treatment at a temperature above about 150 0, preferably in the range between about 150 and 600 C., preferably between 200 and 450 C. The activating treatment is effected for 30 to 300 minutes. If necessary or desired, air or nitrogen is passed over the catalyst during activation to drive off more rapidly any nitrogen oxides which may be present.

After this treatment, the catalyst is ready for the intended use.

The catalyst may be used in the reaction as dust in a fluidized bed or moving bed. However, it is particularly advantageous to arrange the molded, e.g. granulated or pelletized catalyst in long and wide tubes, i.e. tubes of to m. and preferably 10 to 12 m. in length and to 80, and preferably to mm. in inside diameter.

Example 1 4.2 grams of boric acid (crystallized) and 6 grams of phosphoric acid (7.06 grams of 85% phosphoric acid) were added to 500 ml. of water and the mixture was stirred until the acids were completely dissolved. Then 120 gms. of a SiO product known under the trade name of Aerosil ungepresst (Aerosil uncompressed) were added in portions, The mixture was finally stirred thoroughly and evaporated to dryness on a water bath. The lumpy cake was subsequently crushed mechanically in a ball mill.

1.8 ml. of concentrated nitric acid, 160 ml. of water and 25.7 gms. of Bi(NO -5H O were heated to about 50 C. until the nitrate was dissolved. Then 11.7 gms. of molybdic acid (85%) were added with stirring. Thereafter the dried Aerosil was added with stirring and the mixture was again evaporated to dryness on a water bath.

The lumpy :mass was crushed and the fraction between 1.5 and 4 mm. Was recovered by screening. This fraction was calcined for minutes at 300 C. The bulk weight of the finished catalyst was 352 gms./liter.

250 ml. of this catalyst were filled into a quartz tube of 20 mm. in inside diameter so that the length of the bed was about 80 cm. The quartz tube was arranged in an electrically heated furnace which was controlled by means of a contact thermometer. Downstream of the tube was arranged a water-cooled condenser with a receiver followed by two liquid air traps maintained at -70 C.

When 4 normal "liters/hr. of propylene (as a 62% propylene-propane mixture) mixed with 50 normal liters/ hr. of air (saturated with water vapor at 66 C.) were passed over this catalyst at a temperature of 375 C., 420 gms. of total condensate were obtained per day. Processing of the condensate resulted in 32 gms. of acetic acid, 7 gms. of acetic ester, 11 gms. of formaldehyde, 6 gms. of acetaldehyde. Moreover, 13 gms. of acetone and 2 gms. of acrolein could be found. In addition, certain amounts of carbon dioxide and carbon monoxide had been produced.

Propylene conversion was about 37% while only a minor amount of the propane present was converted.

When a similar catalyst was prepared except that the phosphoric acid was omitted, more than of the reaction products (based on organic compounds produced) consisted of acrolein while the balance comprised acetic acid (10%), acetaldehyde (5%), formaldehyde (15%), and acetic ester (3.5%) as well as several organic compounds. The operating conditions were the same as those used in the preceding experiment.

If the boric acid was omitted in place of phosphoric acid, the proportion of acrolein produced under the same operating conditions increased to 70% based on organic compounds.

Example 2 A further catalyst was prepared in a manner analogous to that used in Example 1 for the first catalyst except that the bismuth component was omitted. At 320 C., the propylene conversion was already 55%. The organic compounds insulated from the liquid reaction product contained 49% of acetic acid, 6% of acetaldehyde, 17% of formaldehyde, 10% of acetic ester and 12% of acetone (all percentages by weight). Moreover, 3% of acrolein was obtained. The balance comprised different organic compound. The proportions of carbon dioxide and carbon monoxide obtained in this experiment were higher than those in the preceding experiment.

Example 3 When using a catalyst having the same composition as that of the first catalyst of Example 1, except that the molybdenum component was omitted, a propylene conversion of only 15% was found at 400 C. The product distribution was similar to that obtained with the first catalyst of Example 1.

Example 4 A catalyst was prepared using the same conditions and amounts of constituents as those used for first catalyst of Example 1 except that the Aerosil proportion was varied. The finished catalyst had the following composition:

Percent P 0 7.3 B 0 4.0 M00 16.8 Bi o 21.0 Aerosil 50.9

4.5 liters of propylene mixed with 55 normal liters of air (saturated with water vapor at 61 C.) were passed over 250 ml. of this catalyst at a temperature of 290 C.

A propylene conversion rate of 25% was found at a reaction temperature of 290 C. The organic compounds produced had the following composition:

Percent Acetic acid 40 Formaldehyde 18 Acetaldehyde Acetic ester 12 Acetone 15 Acrolein 3 The balance comprised various organic compounds. Moreover, certain amounts of carbon dioxide and carbon monoxide were produced.

In the case of another catalyst, an alumina product known under the trade name of P 110 was used in place of Aerosil while the composition was otherwise unchanged. A propylene conversion of 27% was found at a temperature of as low as 270 C. and the composition of the organic compounds was substantially identical with that of the preceding experiment. However, the proportions of carbon dioxide and carbon monoxide were higher.

If the experiment described above was carried out with double the feed rate of propylene, an increase in temperature by C. was necessary to maintain the conversion rate. The proportion of acetic acid dropped to 37% while that of the remaining organic compounds increased to some extent. The production of carbon dioxide and carbon monoxide was somewhat reduced. When this experiment was carried out in a suitable pressure apparatus (stainless steel tube of 16 mm. in inside diameter) under a pressure of 4 kg./ sq. cm., the propylene conversion increased to The production of acetic acid and acetaldehyde dropped to a minor extent While the pro duction of the remaining compounds increased correspondingly.

Example 5 When the first catalyst of Example 1 was produced with half of the amount of boric acid and phosphoric acid, activity and product composition remained substantially unchanged under the working conditions described in Example 1. The production of acrolein was slightly higher.

Analogous results were obtained when half the amount of phosphoric acid or boric acid was used. In both cases,

the production of acrolein increased slightly. Moreover,

the amount of acetic acid decreased by 2-3 grams.

Example 6 Percent Acetic acid 51 Acetaldehyde 5 Formaldehyde 15 Acetone 8 Acetic ester 6 Acrolein 5 in addition to small amounts of other organic compounds.

Example 7 A catalyst similar to the first catalyst of Example 1 was prepared as follows: The quantities desired of molybdic acid and bismuth nitrate and 36 ml. of concentrated nitric acid were dissolved in 500 ml. of water. Then a silica product known under the trade name of Aerosil X 200 was added with stirring and the mixture was evaporated on a water bath. The cake was crushed mechanically, mixed with a solution of boric acid and phosphoric acid in 250 ml. of water and the mixture was again evaporated on the water bath. This was followed by drying for 24 hours at 120 C., crushing, recovering the fraction from 2 to 5 mm. by screening, and calcining for 60 minutes at 300 C.

When 5 liters/hr. of propylene (98%) mixed with 60 normal liters/hr. of air (saturated with water vapor at 75 C.) were passed over 250 ml. of the catalyst at a temperature of 340 C., a propylene conversion of 30% was found. The main product again consisted of Percent Acetic acid 53 Acetaldehyde 5 Formaldehyde 19 Acetic ester 7 Acetone 6 Acrolein 6 and further organic compounds. Part of the propylene had been oxidized to form CO and CO.

Example 8 In accordance with Example 1, a catalyst is prepared having the following composition:

Percent B 0 2.0 P 0 4.5 M00 13.4 Bi O 20.6 Aerosil (trade name Ox 200) 59.5

The temperature of calcination is 350 C., and time of calcination is 90 minutes.

Using an apparatus corresponding to Example 1, 5.3 normal liters isobutylene (more than 98%) is passed through 250 cm. of this catalyst. Simultaneously normal liters of air (saturated by steam at C.) is passed through the catalyst. Reaction temperature is 285 C. Following those operating conditions, a conversion of 37% isobutylene has been found. In working up the whole of condensed products there were found:

G. Acetic acid and acrylic acid Ethylacetate 15 Formaldehyde 17 Acetaldehyde l1 Apart from these compounds there were 10 g. acetone and small quantities of methylacrolein in the product.

A certain portion of reacted isobutylene has been oxidized to carbon dioxide and carbon monoxide.

The percentage and parts set forth herein are on a weight basis, unless otherwise indicated.

The amount of molybdenum oxide ranges from 5 to 60% by weight, dependent upon the weight of the total catalyst inclusive the carrier, an amount of 10' to 30% being preferred.

The amount of bismuth oxide ranges from 1 to 30% by weight, dependent upon the weight of the total catalyst inclusive the carrier, an amount of 10 to 30% being preferred.

Heavy metal oxides other than molybdenum oxide and bismuth oxide can be used in the amounts indicated for molybdenum oxide and bismuth oxide, and catalyst compositions for such other heavy metal oxides can be prepared in accordance with the foregoing examples.

The beneficial properties of the catalyst of the invention are indicated above; further indications will be found in Patent 3,255,238 (Ser. No. 214,521, filed Aug. 3, 1962).

What is claimed is:

1. A catalyst useful for oxidation of lower aliphatic olefins to produce therefrom substantial amounts of saturated aliphatic products, said catalyst consisting essentially of a catalyst support bearing the combination molybdenum oxide and bismuth oxide, and phosphoric acid and boric acid in the activated state of calcination of said com- 7 bination at 150600 C. for 30300 minutes, the phosphoric acid and boric acid figured respectively as P 0 and B 0 being about 125% of the total catalyst and the mol proportion of boric acid to phosphoric acid being in the range of about 5:1 to 1:5.

2. A catalyst according to claim 1, wherein the amount of molybdenum oxide is in the range from 5 to 60% by weight of the total catalyst.

3. A catalyst according to claim 1, wherein the amount of molybdenum oxide is in the range from 10 to 30% by weight of the total catalyst.

4. A catalyst according to claim 1, wherein the amount of bismuth oxide is in the range from 1 to 30% by weight of the total catalyst.

5. A catalyst according to claim 1, wherein the amount of bismuth oxide is in the range from 10 to 30% by weight o f the total catalyst.

6. A catalyst according to claim 1, wherein the mol proportion of molybdenum oxide to bismuth oxide is in the range of about 1:3 and 110.3.

7. A catalyst according to claim 1, wherein the support is selected from the group consisting of silica and alumina.

References Cited UNITED STATES PATENTS DANIEL E. WYMAN, Primary Examiner.

OSCAR R. VERTIZ, Examiner.

L. G. MANDONI, L. G. XIARHOS, A. J. GREIF,

Assistant Examiners. 

